1. Field of the Invention
This invention relates to a method for adjusting aggregation size based on ACKnowledgement (ACK) bitmap, and more particularly to a method of dynamic aggregation size adjustment during frame aggregation in a network communication.
2. Description of Related Arts
The IEEE 802.11n standard defines two types of aggregation, Aggregate Media Access Control (MAC) Service Data Unit (A-MSDU) and Aggregate MAC Protocol Data Unit (A-MPDU). The A-MPDU aggregation combines multiple MAC protocol data units (MPDU) in a single PHYsical layer (PHY) Protocol Data Unit (PPDU) frame and transmits it in a single channel access. The size of the PPDU constructed by A-MPDU aggregation has upper bounds either 64 Kbytes or 64 MPDUs, the one reached earlier.
The 802.11n standard defines a Compressed Block Acknowledgment (CBA) to acknowledge the A-MPDU frame. The CBA is a variation of the block acknowledgment introduced by 802.11n in order to acknowledge the aggregate A-MPDU frames with a single ACK frame. The CBA frame contains a bitmap field of 64 bits. Each bit of the bitmap acknowledges one MPDU of the A-MPDU frame. The corrupted MPDU will be indicated by a zero in the bitmap while the successfully received MPDU will be indicated by one. The corrupted MPDUs in the A-MPDU frame will be retransmitted in subsequent transmissions. The CBA bitmap can be read as a clear map of the current channel condition.
It is recommended to send A-MPDU frame with large number of MPDUs if the channel is error free, but if the channels of high Bit Error Rate (BER) large number of these MPDUs will be corrupted and marked in the CBA bitmap for retransmission. Sending A-MPDU of large number of MPDUs in environment with high error rate probability will lead to wasting the channel time and degrading the network performance. Many analytical and simulation works have been carried out in order to estimate the optimal frame size that would increase the throughput and reduce the delay under different network conditions.
Accordingly, it can be seen in the prior arts that there exists a need to provide a method for dynamically adapts the A-MPDU aggregation size to the current state of the channel. The channel conditions can be read from the CBA bitmap of the previous frames transmissions without requiring additional data transmission.